Wrong ROI Ellipse rotation angle documentation?

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Effesian
Effesian on 30 Nov 2021
Commented: Effesian on 30 Nov 2021
Hello,
I am using the roi = drawellipse command from the image processing toolbox (https://www.mathworks.com/help/images/ref/drawellipse.html) to label some elliptical shapes in image.
This returns an Ellipse (roi) object. One property is the "Rotation angle" which according to the documentation (retrieved 30.11.2021) is:
  • Rotation angle of the ROI, specified as a number. The angle is measured in degrees in a clockwise direction around the center of the ROI.
However, if I rotate by hand the ellipse in a COUNTER clockwise direction, the angle increases (thus the angle is measured in degrees in a counter clockwise direction). Is this a typo in the documentation or am I missing something?
Thanks!
I am using:
MATLAB Version: 9.9.0.1467703 (R2020b)

Accepted Answer

Matt J
Matt J on 30 Nov 2021
Edited: Matt J on 30 Nov 2021
In the coordinate conventions of the Image Processing Toolbox, the Y-axis points downward and the Z-axis is pointing into the screen. Therefore, what you would normally consider a counter-clockwise rotation is, in the toolbox's coordinate system, a clockwise rotation about the Z-axis.

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